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Riojasaurus (meaning "Rioja lizard") was a herbivorous sauropodomorph dinosaur named after La Rioja Province in Argentina where it was found by José Bonaparte. It lived during the Late Triassic and grew to about 10 metres (33 ft) long. Riojasaurus is the only known riojasaurid to live in South America.


Riojasaurus had a heavy body, bulky legs, and a long neck and tail. Its leg bones were dense and massive for an early sauropodomorph. By contrast, its vertebrae were lightened by hollow cavities, and unlike most early sauropodomorphs, Riojasaurus had four sacral vertebrae instead of three. It has been thought it probably moved slowly on all fours and was unable to rear up on its back legs. The nearly equal length of the fore and hindlimbs has also been interpreted as suggestive of an obligatorily quadrupedal gait. However, in 2016, Scott Hartman found the hand anatomy, relatively straight back and largely immobile shoulder girdle of Riojasaurus supported it being a biped.

No skull was found with the first skeleton of Riojasaurus, although a well-preserved skull attributed to Riojasaurus' was found later. The teeth of Riojasaurus were leaf shaped and serrated. The upper jaw contained 5 teeth at the front, with 24 more behind them in a row that ended under the eyes.

Comparisons between the scleral rings of Riojasaurus and modern birds and reptiles suggest that it may have been cathemeral, active throughout the day at short intervals.


Riojasaurus is known as a herbivore, like all the other sauropods, but some used to believe that the Riojasaurus was carnivorous, eating off of dead animals, and possibly killing and eating other herbivores. Sharp teeth were found near the bones, leading scientists to believe that they actually had sharp teeth for hunting and killing other animals. But this was proven false, as it was likely that it was simply teeth from a carnivore which has fallen off when it was eating the sauropod.[1]

In The Land Before Time

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A Riojasaurus in the background.

In The Land Before Time V: The Mysterious Island, a Riojasaurus can briefly be seen in a field near the end of the film, in the temporary paradise the herds moved to while waiting for the Great Valley to regrow.